Ink jet printers typically include an ink path from an ink supply to a nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electro statically deflected element. A typical printhead has an array of ink paths with corresponding nozzle openings and associated actuators, such that drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the printhead and a printing substrate are moved relative to one another. In high performance printheads, the nozzle openings typically have a diameter of 50 microns or less, e.g. around 35 microns, are separated at a pitch of 100–300 nozzle/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters or less. Drop ejection frequency is typically 10 kHz or more.
Hoisington et al. U.S. Pat. No. 5,265,315, describes a printhead assembly that has a semiconductor body and a piezoelectric actuator. The body is made of silicon, which is etched to define ink chambers. Nozzle openings are defined by a separate nozzle plate, which is attached to the silicon body. The piezoelectric actuator has a layer of piezoelectric material, which changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber located along the ink path. Piezoelectric ink jet print assemblies are also described in Fishbeck et al. U.S. Pat. No. 4,825,227, Hine U.S. Pat. No. 4,937,598, Moynihan et al. U.S. Pat. No. 5,659,346, and Hoisington U.S. Pat. No. 5,757,391, the entire contents of which are hereby incorporated by reference.
Printing accuracy of printheads, especially high performance printheads, is influenced by a number of factors, including the size and velocity uniformity of drops ejected by the nozzles in the printhead. The drop size and drop velocity uniformity are in turn influenced by a number of factors, such as, for example, the contamination of the ink flow paths with dissolved gasses or bubbles. Deaeration of ink is described in Hine et al. U.S. Pat. No. 4,940,955, Hoisington, U.S. Pat. No. 4,901,082, Moynihan et al. U.S. Pat. No. 5,701,148, and Hine U.S. Pat. No. 5,742,313, the entire contents of all of which is hereby incorporated by reference.